OpenAPI (Swagger Specification) — HTTP API

The REST style leaves a lot of decisions up to the developers.

On the one hand, the task of REST is not to set a specification but to define the principles that allow you to build a good HTTP API. In this sense, REST is a well-thought-out concept, doesn't depend on trends, and has existed for decades without change.

On the other hand, it has the freedom in:

• How links are organized
• What data structures are sent
• How data is returned

It means all REST APIs are quite different and sometimes quite strong.

It leads to a large number of problems, which are easily solvable in the RPC protocols:

• The documentation is described manually and is different in each API
• There's no automatic way to verify if API passes calls and parameters correctly
• The language doesn't generate test code or data structures to work with API data
• There's static analysis, such as highlighting incorrect queries in the editor

The OpenAPI standard solves these and other issues. It is a simple and language-independent way to describe the API in a format that both machines and humans can understand. Programmers use it to automatically generate documentation, tests, and code for executing queries and checking the correctness of data:

# OpenAPI descriptions are best written in YAML format
# Example using a pet store

openapi: "3.0.0"
info:
  version: 1.0.0
  title: Swagger Petstore
  license:
    name: MIT
servers:
  - url: http://petstore.swagger.io/v1
paths:
  /pets:
    get:
      summary: List all pets
      operationId: listPets
      tags:
        - pets
      parameters:
        - name: limit
          in: query
          description: How many items to return at one time (max 100)
          required: false
          schema:
            type: integer
            format: int32
      responses:
        '200':
          description: A paged array of pets
          content:
            application/json:
              schema:
                $ref: "#/components/schemas/Pets"
    post:
      summary: Create a pet
      operationId: createPets
      tags:
        - pets
      responses:
        '201':
          description: Null response
  /pets/{petId}:
    get:
      summary: Info for a specific pet
      operationId: showPetById
      tags:
        - pets
      parameters:
        - name: petId
          in: path
          required: true
          description: The id of the pet to retrieve
          schema:
            type: string
      responses:
        '200':
          description: Expected response to a valid request
          content:
            application/json:
              schema:
                $ref: "#/components/schemas/Pet"
components:
  schemas:
    Pet:
      type: object
      required:
        - id
        - name
      properties:
        id:
          type: integer
          format: int64
        name:
          type: string
        tag:
          type: string
    Pets:
      type: array
      items:
        $ref: "#/components/schemas/Pet"

Here we can see a set of endpoints that define the structure of the parameters expected to be input and the output data. Using this description and the relevant libraries for each language, we can generate documentation, test code, the necessary classes to store this data, and even a library to perform queries to this API.

Recommended materials

1. OpenAPI Specification